Metal treatment



' Patented June 8, 1937 UNITED STATES METAITTREATMENT Michael W. Freeman, Detroit, Mich.

No Drawing.

Application February 15, 1932 Serial No. 593,209

Claims.

The present invention relates to composition for and process of pickling metallic surfaces such as iron, steel, copper, bronze, various alloys, and others, for removing rust, mill scale, handling 5 marks, and oxides of various natures.

In the prior art, it has been customary to use a mineral acid bath for pickling of metals and such mineral acids as sulphuric acid, muriatic acid, and the like, have been employed. When using such mineral acid baths for pickling purposes, it is usually, if not always, necessary to include in the bath an inhibitor which materially adds to the cost of the metal treatment.

The life of the ordinary mineral acid pickling bath is relatively short due to the formation of salts in the bath which causes the bath to lose its effectiveness. The bath cannot be indefinitely fortified because of the formation of the salts which interferes with satisfactory pickling. For

example, when the percentage of the metal salts approximates the percentage of the free mineral acid, the bath must be discarded.

Also, when using the customary mineral acid bath, it is highly important that,.upon removal of the metal from the pickling bath, the metal be thoroughly washed or otherwise cleaned, and in some processes this washing is done with a water or an alkaline solution to remove the acid and prevent further action upon the metal. Even 3() with careful washing and the attempted neutralization of the film of acid bath remaining on the metal, it is an established fact that the action is not stopped and in fact the metal quite readily rusts or corrodes within a 'very short time after 35 removal from the bath.-

It has been recognized for years in the steel industry that the so-called pickling processes used for the removal of mill scale, iron rust, and the like, from steel or other metal products not 40 only result in considerable waste, but detrimental effects in many cases result due to the rapid solution of the metal when the pickling bath is effective. Due to the relatively rapid attack upon the surfaces, an ununiform treatment of the metal is 45 obtained and often pin holes and roughened surfaces are formed. Also, by reason of the formation of pockets of hydrogen gas between the layers of the scale and the metal itself, the metallic object is affected, bringing about an undesirable 50 brittleness. I

An important object of the present invention is to provide a pickling bath which will reduce to a minimum or entirely eliminate the many objectionable features of the prior art pickling'baths. 55 More specifically, the invention contemplates the employment of a solution of an organic sulphonic acid, or mixtures thereof, capable of giving satisfactory pickling results.

Another important object of the invention is to provide a pickling bath substantially, if not entirely, devoid of mineral acids, and in this connection make use of a water solution of an organic sulphonic acid bath in which the metal to be pickled may be placed, and due to the uniform action of the water solution of the sulphonic acid, less metal is actually dissolved, giving a smoother finished surface and consequently wasting less of the metal in the pickling solution without shortening the time customarily required with the more active mineral acid baths for the same class of work. It also may be pointed out that due to the lower activity of my improved pickling bath, the surface of the metal is substantially devoid of irregularities or pitted surfaces usually obtained in cleaning metals in the ordinary mineral acid pickling baths under the same conditions.

The present invention resides broadly in the use of a water solution of an organic sulphonic acid or mixture thereof as a pickling bath as above set forth, and is in no way limited to any particular method of obtaining the organic sulphonic acid or the apparatus used in the carrying out of the pickling process.

Broadly speaking, the organic sulphonic acids can roughly be divided into two groups: one, the aromatic hydrocarbons, and the other the allphatic hydro-carbons. This invention contemplates not only the use of both the sulphonic acids of the aromatic and aliphatic hydro-carbons, but also the derivatives of the organic sulphonic acids of the aromatic and aliphatic series of hydro-carbons. For example, I have obtained very satisfactory results with a water solution of benzene sulphonic acid, the benzene sulphonic acid being sulphonic acid of the aromatic hydrocarbon series. I have also obtained very satisfactory results with a water solution of chlorobenzene sulphonic acid, the chloro-benzene sulphonic acid being a derivative of the benzene sulphonic acid.

From the practical standpoint, it is most desirable to use an organic sulphonic acid of the arcmatic hydro-carbon series or derivatives thereof because aromatic hydro-carbons or their derivatives are much more readily sulphonated and therefore 'more economical to prepare. Although I consider the sulphonic acids of the arcmatic series more desirable for these reasons, nevertheless the sulphonic acids of the aliphatic series can be used, and in fact I have used them To produce such a bath, commercial benzol, which may contain toluene, xylol, phenol, and

other compounds, can be treated in the .follow ing manner: The commercial benzol is sulphonated with concentrated sulphuric acid, the mixture being subjected to elevated temperatures. Starting with a definite weight of concentrated sulphuric acid (100 mole weight) maintained at a temperature of 150 degrees to 1'70 degrees centigrade, commercial benzol is added, either in the liquid or vapor state, until approximately from one-half to three-fourths of the sulphuric acid is reacted with the benzene to form benzene sulphonic acid and traces of other sulphonic acids. To the sulphuric acid, benzene sulphonic acid mixture, commercial naphthalene is then added in sufficient quantities to use up approximately fifty per cent of the remaining free sulphuric acid to form naphthalene sulphonic acid. The remaining free sulphuric acid is then reacted with suflicient crude phenol to give the resulting mixture of essentially benzene, naphthalene, and phenol sulphonic acids substantially free of the mineral acid (sulphuric acid) which, as I have pointed out hereinabove, is undesirable in pickling baths. Instead of the addition of naphthalene and phenol to completely use up the free sulphuric acid, the reaction may be furthered by first adding a dehydrating agent, such as phosphorous penta oxide, and then adding more benzene to the mixture. To then insure against the presence of unreacted sulphuric acid, a suflicient quantity of an organic base such as aniline is added. Instead of using phenol to react with or use up the remaining free sulphuric acid, the addition of equivalent amounts of an organic base such as aniline will accomplish this by combining with the free sulphuric acid to form aniline sulphate at ordinary temperatures, or at elevated temperatures mixtures of aniline sulphate and sulphanilic acid.

The resulting mixture of organic sulphonic acids can then be dissolved in water in varying amounts, with one example being approximately one part of the sulphonic acids to twenty parts of water which forms my improved pickling bath. The conditions under whi '1 this pickling bath works most effectively necessarily depends upon the type of mill scale, iron rust, and the like to be removed and the particular metal being treated. However, under ordinary conditions for mill scale removal, I have found that a temperature of approximately 65 degrees to 70 degrees centigrade gives very satisfactory results. It is obvious that the time required for satisfactory pickling will depend, among other things, upon the concentration and temperature of the pickling bath and upon the type and condition of the surface of the metalto be pickled.

An important feature of a pickling bath formed from an organic sulphonic acid or derivatives and mixtures thereof resides in the fact that whatever salts formed by reason of the pickling of the metal do not adversely affect the pickling operation. For example, considerable salts may form in the pickling bath and notwithstanding the presence of the salts, the effectiveness of the bath is not reduced. When these salts accumulate to the point that they interfere with the capacity of the receptacle in which the pickling is being done, the sludge should be removed and new organic sulphonic acid added to maintaina proper concentration of the pickling bath. With the Work I have done so far, it does not seem that the bath deteriorates with age, and I have been successful in the removal of sludge and addition of new acid.

This pickling bath lends itself admirably well to a continuous process of pickling by simply removing the metal salts of the sulphonic acid as they form and settle to the bottom and subsequently fortifying the pickling solution by the addition of a fresh supply of sulphonic acid. With the customary mineral acid bath, the life thereof is relatively short and the formation of salts reduces the effectiveness of the bath which cannot be adequately restored by the mere addition of new mineral acid, because of the interference of the metal salts of the mineral acids which are formed.

The metal salts of the sulphonic acid which are formed when using my improved pickling bath do not adversely afiect the pickling operation even though the solution becomes very d1- lute, and in fact my pickling bath is effective up to the point of neutrality.

Another very important advantage of my pickling bath resides in the elimination of the necessity for washing or scrubbing of the pickled metal. With the mineral acid bath, the metal should be washed in water or an alkaline solution as above described, while with the use of my bath, it is desirable to leave the thin film of pickling solution remaining on the metal surface intact. I have found that the thin film of my pickling solution remaining on the metal serves as a temporary protection, and within a reasonable lapse of time prevents rusting or other corrosion. This is particularly important where it is not feasible to immediately use the pickled metal upon removal from the pickling bath.

During the treatment of the metal surfaces in the organic sulphonic acid bath, the surfaces are treated uniformly; that is, they do not become pitted or otherwise roughened so that the finished surface is smooth as compared to the surface obtained with the ordinary mineral acid pickling bath under the same conditions.

To determine the effect of my pickling bath on nickel, copper, and chrome, I have placed varying amounts thereof in such baths, and have found that the presence of the organic sulphonic acid does not interfere with nickel, copper, or chrome plating. Furthermore, I have found that the treatment of metal with the organic sulphonic acid bath to be of considerable importance when such metal is to be subsequently galvanized, in that it is not necessary to even remove the pickling solution from the metal before it is placed in the galvanizing bath. As is well known, when pickling or cleaning the surface of metal with the ordinary mineral acid pickling bath in preparation of its surface for galvanizing, various operations have to be resorted to such as careful cleaning by washing or scrubbing the surface of the metal coming from the mineral acid bath to completely remove all traces of the acids and their salts. Following the cleaning operation, the metal has to be thoroughly dried before going to the galvanizing op- 25. mining the proper treatment to give to the metal I claim:

eration. Also, I may point out the advantages of my improved pickling solution over the customary mineral acid bath in that the mineral acid bath wastes-considerable of the metal due to the more rapid action of the acid. Resulting from this rapldsolution of metal are the socalled pickling fumeswhich are dangerous from the standpoint of their poisonous nature as well as fire hazard and deterioration eifect. It will be obvioustothose versed in the art that there are many other uses to which this type of pickling bath 'can be put. I have concommercial metal pieces, and in all cases I have found that the water solutions of the organic sulphonic acids give more satisfactory pickling results than the mineral acid baths.

However, it has been noticed that some organic sulphonic acid pickling baths give the desired pickling more rapidly than others. For example, a bath made with the phenol sulphonic acid works more rapidly than such a bath made with naphthalene sulphonic acid. The question of temperature and time, as well as concentration, are of course important factors in deterto be pickled in any given pickling bath.

1. The process of pickling metallic surfaces such as iron or steel, consisting in treating the surfaces in a bath of organic sulphonic acid substantially free from mineral acid.

2. The process ofpickling metallic surfaces such as iron or steel, consisting in subjecting said surfaces to the action of a bath composed essentially of awater solution of an organic sulphonic acid, said bath being substantially free from mineral acid.

3. The process of pickling metallic surfaces such as iron or steel, consisting in subjecting said surfaces to the action of a heated bath composed essentially of an organic sulphonic acid solution substantially free from mineral acid.

4. A pickling bath for metallic surfaces such as iron or steel, consisting essentially of a water solution of an organic sulphonic acid, which bath is substantially devoid of mineral acid.

5. The process of pickling metallic surfaces such as iron and steel consisting in treating the surface in a bath of organic sulphonic acid substantially free from mineral acid and leaving a film of said sulphonic acid on said surface.

MICHAEL w. FREEMAN. 

